1. Field of the Invention
The present invention relates to a production process for a semiconductor device having metal electrodes such as bumps provided on its surface.
2. Description of Related Art
Some of semiconductor chips have metal electrodes such as bumps projecting from a surface thereof. For example, such a semiconductor chip may be mounted on a printed wiring board by flip-chip bonding, or bonded to another semiconductor chip in a stacked relation to form a semiconductor device of chip-on-chip structure.
In general, the semiconductor chip has an insulating film and an aluminum interconnection film provided on a surface of a semiconductor substrate which serves as a base thereof, and connection pads for external electrical connection provided in proper positions on the surface thereof. A protective film covering the outermost surface of the semiconductor substrate is formed with openings which expose the connection pads therethrough.
A process for forming the bumps generally comprises the steps of: forming a seed film on the entire surface of a wafer formed with a protective film; forming on the seed film a resist film having openings just above the connection pads by patterning; and selectively depositing a metal material for the bumps to a great thickness in the openings formed in the resist film. Thereafter, the resist film is removed, and then the seed film except bump portions thereof is removed. Thus, island-like bumps electrically connected to the respective connection pads are provided.
As can be understood from the foregoing, the formation of the bumps requires complicated steps such as the formation of the resist film on a wafer-by-wafer basis, so that the process involves an increased number of steps thereby hindering the reduction in the production cost of the semiconductor chip.
It is an object of the present invention to provide a production process for a semiconductor device which allows for cost reduction by simplifying the step of forming metal electrodes.
The process according to the present invention is a production process for a semiconductor device having a metal electrode provided on a semiconductor substrate thereof, and comprises the steps of: forming a metal electrode portion on a surface of another substrate for electrode transfer; and transferring the metal electrode portion from the electrode transfer substrate onto the semiconductor substrate by pressing together the electrode transfer substrate and the semiconductor substrate.
In accordance with the invention, the metal electrode portion is formed on the electrode transfer substrate, and then transferred from the electrode transfer substrate onto the semiconductor substrate. Therefore, the step of forming a resist film on the surface of the semiconductor substrate and the step of patterning a seed film on the surface of the semiconductor substrate can be obviated.
The electrode transfer substrate allows for repetitive formation of the metal electrode portions thereon and, hence, can repeatedly be used for a plurality of semiconductor substrates. Therefore, the production process for the semiconductor device is totally simplified thereby to allow for cost reduction.
In accordance with one embodiment of the invention, the electrode transfer substrate has a seed film provided on the surface thereof, and the step of forming the metal electrode portion on the electrode transfer substrate comprises the step of depositing a material for the metal electrode on the seed film by plating.
More specifically, the metal electrode portion is formed by depositing the metal material on the seed film on the electrode transfer substrate by plating (electroplating or electroless plating). In this case, the electrode transfer substrate formed with the seed film can be used again for formation of a metal electrode portion for the next semiconductor device immediately after the metal electrode portion is transferred onto the semiconductor substrate. The formation of the metal electrode on the semiconductor substrate is thus achieved by the formation of the metal electrode portion on the electrode transfer substrate by plating and the transfer of the metal electrode portion onto the semiconductor substrate, thereby drastically simplifying the process as compared with the prior art.
The electrode transfer substrate is preferably covered with a patterning film which exposes therefrom a portion of the seed film in an electrode portion forming position. Thus, the metal electrode material can be deposited only on the properly exposed portion of the seed film. This obviates the need for formation and subsequent removal of a patterning film for pattern-formation of the metal electrode portion on the semiconductor substrate, thereby further simplifying the process.
The electrode transfer substrate preferably has an insulating film which covers the seed film except the portion thereof in the electrode portion forming position.
In this case, the insulating film which serves as the patterning film which exposes therefrom the portion of the seed film in the electrode portion forming position is provided on the electrode transfer substrate, so that the metal electrode material can selectively be deposited on the seed film by electroplating. At this time, there is no need to cover the electrode transfer substrate with an additional patterning film.
The seed film is preferably composed of such a material that the metal electrode portion has a lower adhesion affinity for the seed film than for a portion of the semiconductor substrate on which the metal electrode portion is to be transferred.
In this case, the adhesion between the metal electrode portion and the semiconductor substrate is superior to the adhesion between the metal electrode portion and the seed film. Therefore, when the semiconductor substrate and the electrode transfer substrate are pressed together and then separated from each other, the metal electrode portion can assuredly be transferred onto the semiconductor substrate. Thus, the formation of the metal electrode on the semiconductor substrate can advantageously be achieved.
The electrode transfer substrate may be composed of a transparent material, and the seed film may locally be present in the electrode portion forming position on the electrode transfer substrate.
With this arrangement, when the electrode transfer substrate is joined with the semiconductor substrate, the semiconductor substrate and the seed film can be viewed from a rear side of the electrode transfer substrate (which is opposite from a side thereof on which the metal electrode portion is formed). Since the seed film is locally present in the electrode portion forming position on the electrode transfer substrate, the electrode transfer substrate can properly be positioned with respect to the semiconductor substrate by monitoring the position of the seed film and an electrode forming position on the semiconductor substrate from the rear side of the electrode transfer substrate by proper image pick-up means. This ensures precise transfer of the metal electrode portion.
A protective film having an opening which exposes therethrough an electrical contact portion of the semiconductor substrate may be provided on the semiconductor substrate. In this case, it is preferred that the metal electrode portion is formed in a position on the electrode transfer substrate corresponding to the position of the electrical contact portion in the step of forming the metal electrode portion on the electrode transfer substrate, and the metal electrode portion is transferred onto the electrical contact portion in the step of transferring the metal electrode portion.
Thus, the metal electrode can be provided on the electrical contact portion exposed from the protective film on the semiconductor substrate.